By Mark Fritch
Featured in: ILBA Log Building News #34
Based on: ILBA conference presentation by Dalibor Houdek, Fornitek Canada Corporation
Dalibor began his presentation by saying, “First, wood doesn’t burn; it is a good insulator.” He clarified that as heat is applied there is thermal degradation that causes wood to give off gases, and it is the gases that are flammable.
Dalibor, working on his PhD at the Technical University of Zvolen, Slovakia, built a furnace that applied heat to one side of 11-inch diameter scribe-fit logs, in which the long grooves averaged 50 mm (2”) wide. The logs were kiln-dried spruce at 19% moisture content.
Fire resistance is defined as the ability of a wall system to withstand exposure to high temperatures without collapse – and so a vertical load was applied to the top of the test walls.
The walls were equipped with thermocouples and monitored as heat was applied to one side – the ISO 384 standard test. For 45 minutes heat was applied to one side – and it reached 700º C (1,300º F). No flames penetrated the wall during the test, and there was no structural failure.
The thermocouples showed there was no measurable increase in temperature on the side of the wall opposite the furnace. In fact, once the heat source was removed, the log walls stopped burning on their own in just two minutes.
Dalibor then showed a dramatic video of the large-scale burn test. A scribe-fit wall panel about 8-feet square was built, and a heat source applied flame to one side of the wall. The wall was preloaded with a fixed load and rigged with thermocouples.
After three hours there was no penetration of flames through the wall. The temperature on the side with the furnace was 1,100º C (2,000º F), and the highest temperature reached on the other side was just 32º C (90º F).